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Sewer or septic line replacement: placing the new pipe in the trench. This article describes how the new sewer line is installed when a sewer pipe or "drain line" is replaced. We present an actual case study, illustrated with photos of each step in the diagnosis and replacement of a blocked sewer line. Also see Backups and Clogged Drains diagnosing septic backups and septic system failures versus clogged drains.

Guide to installing the replacement sewer pipe line

Safety of occupants and neighbors during excavation for sewer line repairs

When the plumbers left the site we had created a hole which was a trip hazard to folks who might cross the yard.

While our immediate makeshift hazard indicators
(nearby wood fence scraps and a laundry basket) was amateur and insecure, at least
we had an immediate visual indicator that there was something here to watch out for.

We then went in search for some more sturdy materials to cover the hole until
further repair work could begin.

Safety during sewer line trench excavation

Also amateur
but successful at warning people about the risk of falling into a ditch.

Do not leave any site excavations open and unattended: the risks are injury as someone may fall in, and in freezing climates there may be a risk of piping freeze damage.

What is the proper slope for sewer lines between house and septic tank or sewer main?

Sewer line trenches should be as uniform in slope as possible and should slope between 2% and 10% grade - that is, the sewer line slope can drop between two feet and ten feet per one hundred feet of run. [4]

You can see that the sewer line slope down this hillside is excessive. A risk (less in plastic pvc than in cast iron pipes) is that the water and the solids in the sewage don't remain together, leaving solids behind to clog the piping. Also the wastewater flowing into the septic tank at the bottom of the hill is really zooming in velocity - making the condition of the septic tank inlet baffle even more important.

Sewer Line Trench Details: uniformity, soil compaction

If you don't want sagging or broken sewer line pipes, clogs, and failures in the piping, then the sewer line trench bottom should be properly and uniformly sloped and compacted. The bottom of the sewer line trench should be virgin soil - not over-excavated. But since excavating is a rough art, some trench sections may be uneven and deeper than others. In that case the soil used for fill beneath the sewer piping must be adequately compacted to avoid future sags.

If you place the sewer piping in soft fill or areas where the fill compaction varies, the risk is that the piping develops low spots, sags, even breaks, leading to future clogging. And if trenches are not below the frost line, wastewater sitting in a low pipe sag in freezing climates may freeze, totally blocking the system.

The Alaska Septic Installation Manual suggests that sewer line trenches should be as narrow as possible in width and that piping should be laid on undisturbed soil or on compacted backfill soil. [4]

Installing the replacement sewer line

Installing and connecting the new drain sections

Sewer line diameter

The minimum diameter sewer line piping allowed in most jurisdictions (and Alaska) is 4-inches in diameter. Smaller lines are prone to clogging. We are referring to gravity-flow sewer lines here. A pumped or forced sewer main is usually carrying sewage that has been through a grinder pump and as a result, in residential applications smaller diameter piping may be allowed.

Sections of the new drain were laid along the trench for installation, cut to
length at either end, and then connected together. Note the grease used to slip the sections of drain pipe together.

At the up-hill house end, we connected the new drain line to the existing stub of cast iron sewer
line outside of the house foundation wall.

This avoided the cost and trouble of having to break through
the foundation wall to install a new line into the home, and avoided possible damage to the nearby
heating boiler.

The rubber coupling used to connect the two drains leaked and had to be re-connected.

These couplings
work fine, durably, and reliably provided the pipes they connect are lined up carefully. An askew
pipe connection is more likely to leak.

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Document Sources used for this web page include but are not limited to: Agricultural Fact Sheet #SW-161 "Septic Tank Pumping," by Paul D. Robillard and
Kelli S. Martin. Penn State College of Agriculture - Cooperative Extension, edited and annotated by
Dan Friedman (Thanks: to Bob Mackey for proofreading the original source material.)

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

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Builder's Guide to Wells and Septic Systems, Woodson, R. Dodge: $ 24.95; MCGRAW HILL B; TP;
Quoting from Amazon's description: For the homebuilder, one mistake in estimating or installing wells and septic systems can cost thousands of dollars. This comprehensive guide filled with case studies can prevent that. Master plumber R. Dodge Woodson packs this reader-friendly guide with guidance and information, including details on new techniques and materials that can economize and expedite jobs and advice on how to avoid mistakes in both estimating and construction. Chapters cover virtually every aspect of wells and septic systems, including on-site evaluations; site limitations; bidding; soil studies, septic designs, and code-related issues; drilled and dug wells, gravel and pipe, chamber-type, and gravity septic systems; pump stations; common problems with well installation; and remedies for poor septic situations. Woodson also discusses ways to increase profits by avoiding cost overruns.

Country Plumbing: Living with a Septic System, Hartigan, Gerry: $ 9.95; ALAN C HOOD & TP;
Quoting an Amazon reviewer's comment, with which we agree--DF:This book is informative as far as it goes and might be most useful for someone with an older system. But it was written in the early 1980s. A lot has changed since then. In particular, the book doesn't cover any of the newer systems that are used more and more nowadays in some parts of the country -- sand mounds, aeration systems, lagoons, etc.